1. Field of the Invention
The present invention relates generally to a system and method for polishing a metal surface formed on a semiconductor device.
2. Description of Related Background Art
Processes for producing semiconductor wafers (which will be referred to as xe2x80x9cwafersxe2x80x9d) include a process called CMP (chemical mechanical polishing). This CMP process is mainly used for polishing a layer of tungsten oxide in a semiconductor device which is formed by multi-layer metallization. This is a method for dropping an abrasive solution including mechanical and chemical polishing particles onto a surface of an abrasive cloth, which is an abrasive member, and for pressing a polished surface of the wafer against the abrasive cloth to remove a part of the polished surface.
In a conventional CMP process, in a system shown in, e.g., FIG. 9, a wafer W held by a wafer holding mechanism 13 is pressed against a rotating table 12, on which an abrasive cloth 11 serving as an abrasive layer has been formed, at a predetermined pressure. While an abrasive solution is supplied from a nozzle 14 to the surface of the abrasive cloth 11, the rotating table 12 is rotated, and the wafer holding mechanism 13 is rotated by a motor 15. Thus, the wafer W is caused to rotate on the rotating table 12 and to relatively revolve, so that the surface of the wafer W is polished. As the abrasive cloth 11, a foam resin, such as urethane foam, having a thickness of, e.g., about 1.2 mm, is used, and as the abrasive solution, a slurry, wherein silica (SiO2) serving as mechanical polishing particles, and chemical polishing particles are dispersed in a solution, is used.
For example, the surface of the abrasive cloth 11 is dressed by a finishing member of diamond, on which fine protruding portions are formed, every time the wafer W is polished. Thus, the surface of the abrasive cloth 11 recovers its polishing capacity. On the other hand, the mixture and reaction products of the slurry (abrasive solution) with tungsten oxide, which are produced by the polishing, adhere to the surface of the abrasive cloth 11. The mixture and reaction products are removed by supplying, e.g., pure water, when the dressing is carried out, since the mixture and reaction products are dissolved in water.
By the way, in recent years, a technique for forming a copper wiring by a damascene process is widely noticed. This process requires a CMP process.
Conventionally, even if the mixture and reaction products of the slurry (abrasive solution) with tungsten oxide, which are produced by the polishing, adhere to the surface of the abrasive cloth 11, the mixture and reaction products can be removed only by supplying, e.g., pure water, when the dressing is carried out by the finishing member of diamond, since the mixture and reaction products are dissolved in wafer.
However, in the CMP process when forming a copper wiring by the damascene process, reaction products produced by a reaction of copper with a slurry, which is suitably used, are difficult to be dissolved in pure water due to the characteristics of the slurry. For that reason, the reaction products can not be removed by the same dressing as that in the case of tungsten oxide.
Referring to FIG. 10, this state will be explained. Irregularities 16 are formed on the surface of the abrasive cloth 11 by the dressing, and particles 17 of the above described reaction products come into spaces of the irregularities 16. In addition, the particles 17 also come into foam portions 18. These particles 17 remain without being washed.
If the reaction products produced at the polishing step thus adhere to the surface of the abrasive cloth, the polishing capacity deteriorates, and the uniformity of the polished surface also deteriorates. For that reason, the number of scans on the surface of the abrasive cloth by diamond has been increased to remove the reaction products. However, if the number of the scans is increased, the scraped portion of the abrasive cloth at the polishing step for a single wafer W increases to shorten the life of the abrasive cloth, and throughput lowers since the time required to carry out the finishing operation increases.
It is therefore an object of the present invention to eliminate the aforementioned problems and to remove reaction products, which adhere to an abrasive member after a substrate is polished, in a short time.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, a polishing system comprises: polishing unit that polishes a metal constituting a polished surface of a substrate by supplying an abrasive solution having a chemical abrasive function to a polishing surface of an abrasive member while relatively sliding the polished surface and the abrasive member; chemical supply unit that supplies a chemical, which dissolves a reaction product produced by a reaction of the metal with the abrasive solution, to the polishing surface of the abrasive member; polishing surface finishing unit that scraps the polishing surface to recover a polishing capacity of the abrasive member by supplying a finishing fluid to the polishing surface while relatively sliding on the polishing surface of the abrasive member; and cleaning unit that supplies a cleaning solution to the polishing surface to remove the chemical from the polishing surface.
With this construction, the reaction product produced by the reaction of the metal constituting the polished surface with the abrasive solution can be dissolved in the chemical, and the abrasive member can be scraped by the polishing surface finishing member. Therefore, the polishing capacity of the abrasive member can be recovered in a short time, and the life of the pad can be increased.
This construction is effectively used if copper is used as the metal when the reaction product produced by the reaction of the metal with the abrasive solution is difficult to be dissolved in water.
The finishing fluid may be the chemical, and the polishing surface finishing unit may relatively slide on the polishing surface of the abrasive member while the chemical supply unit supplies the chemical to the polishing surface of the abrasive member.
By using the chemical as the finishing fluid, the polishing surface finishing unit can relatively slide on the polishing surface of the abrasive member while the chemical supply unit supplies the chemical to the polishing surface of the abrasive member, so that it is possible to efficiently carry out both of the dissolution of the reaction product in the chemical and the recovery of the polishing capacity of the abrasive member.
Alternatively, the finishing fluid may be the cleaning solution, and the polishing surface finishing unit may relatively slide on the polishing surface of the abrasive member while the cleaning unit supplies the cleaning solution to the polishing surface of the abrasive member.
By using the cleaning solution as the finishing fluid, the polishing surface finishing unit can relatively slide on the polishing surface of the abrasive member while the cleaning unit supplies the cleaning solution to the polishing surface of the abrasive member, so that it is possible to dissolve the reaction product in the chemical and it is possible to efficiently carry out both of the removal of the chemical from the polishing surface and the recovery of the polishing capacity of the abrasive member.
The cleaning unit may have a discharge nozzle for discharging the cleaning solution, which has been pressurized, to the polishing surface of the abrasive member.
Thus, the chemical supplied to the surface of the substrate can be surely removed in a short time.
The chemical may contain any one of oxtail acid, citric acid and ammonia.
The abrasive solution may contain any one of silica (SiO2) alumina (Al2O3), hydrogen peroxide (H2O2) and phthalic acid.